1. Field of the Invention
This invention relates to a precision apparatus for measuring and mixing volumes of two or more liquids.
2. Description of the Prior Art
In the manufacture of synthetic thermoplastic fiber materials, such as polyamides, polyesters, or polyolefins, it is common practice to apply a finish liquid (also known as a "spin finish") to the surface of the fibers. The spin finish may be applied using any of a variety of mechanical expedients, such as a metered tip applicator, a rotary kiss roller, or a metered spray applicator.
The finish liquid is commonly formulated in an area remote from the area housing the fiber spinning machines. The finish liquid is formulated by measuring and them mixing a predetermined volume of each of several finish components in a preferred order, the last of these being a diluent liquid. For economy, one relatively large volume mixing tank is typically dedicated to the finish preparation for a plurality of spinning machines. This arrangement has certain disadvantages.
Storing a large volume of liquid material in a single mixing tank enhances the possibility of bacteria growth. In addition, since a single mixing tank is used to service a multiple number of spinning machines, each machine would receive a "standard" finish mixture as prepared in that tank. When, as occurs from time-to-time, changes are made to a given finish formulation, unused quantities of previously formulated finish mixtures may result. Moreover, if a mixture different from the standard would be preferable for a fiber being produced by a given spinning machine, a separate mixing tank would be dedicated solely to that different mixture. Owing to the size and space occupied by the mixing tanks it is believed to be economically impractical to allocate a finish mixing tank to a spinning machine on a one-to-one basis.
There have been attempts in the art to overcome these problems using a so-called "just-in-time" smaller-volume batch diluter apparatus that is located near a the spinning machine. Typical devices use spring-loaded flow regulators, such as the Kates Flow Regulator, manufactured by W. A. Kates Company, Ferndale, Mich. These spring-loaded devices are economical, but are subject to loss of accuracy should the supply pressures drop below a critical minimum, or if the supply stream viscosity changes so as to significantly affect the pressure drop through the device. A more elaborate and costly device, such as the Henkel In-line Mixer, manufactured by Henkel Corporation, Charlotte, N.C., uses another flow sensing and flow control valve scheme to reduce the sensitivity to supply pressure or viscosity changes.
In any case, devices which rely on flow measurement and control are subject to inaccuracies during start-up where flow phenomena, such as pressure transients and flow acceleration, create a non-steady-state condition. This disadvantage can be overcome by either diverting the start-up flow to waste, or by blending it with large quantities of accurately diluted finish. By using large volume tanks so that these diluter apparatus have longer steady-state run times, the inaccurately measured volumes of liquids during start-up transient periods are small in proportion to the more accurate volumes measured during steady-state running periods. Assuming good mixing in a sufficiently large tank, the average composition of the finish can be maintained within acceptable limits.
In view of the foregoing it is believed to be advantageous to provide a volumetric mixing apparatus adapted to prepare in a precision manner a finish liquid mixture particularized for an associated spinning machine.